From 1d069811e361dc17eb2fd51b22ca1a8ccf0ca353 Mon Sep 17 00:00:00 2001
From: SashegDev <gdsasheg@gmail.com>
Date: Mon, 13 Jul 2026 13:32:34 +0000
Subject: [PATCH] =?UTF-8?q?fix:=20Forge/NeoForge=20split-package=20Resolut?=
 =?UTF-8?q?ionException=20=E2=80=94=20skip=20version=20jar=20on=20classpat?=
 =?UTF-8?q?h,=20fix=20${classpath}=20variable=20resolution?=
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---
 .../launch/LaunchCommandBuilder.java          | 31 ++++++++++++++-----
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/launcher/launcher/src/main/java/sashegdev/zernmc/launcher/minecraft/launch/LaunchCommandBuilder.java b/launcher/launcher/src/main/java/sashegdev/zernmc/launcher/minecraft/launch/LaunchCommandBuilder.java
index 6990037..da05ce9 100644
--- a/launcher/launcher/src/main/java/sashegdev/zernmc/launcher/minecraft/launch/LaunchCommandBuilder.java
+++ b/launcher/launcher/src/main/java/sashegdev/zernmc/launcher/minecraft/launch/LaunchCommandBuilder.java
@@ -86,14 +86,19 @@ public class LaunchCommandBuilder {
                     classpath = filterClasspathAgainstModulePath(classpath, manifest.getJvmArguments());
                 }
                 command.add("-cp");
-                command.add(writeClasspathFile(classpath));
+                String cpFile = writeClasspathFile(classpath);
+                command.add(cpFile);
 
                 // Add JVM arguments from version.json manifest
                 // Includes -DignoreList, -p (module path), --add-modules, --add-opens,
                 // and -DlibraryDirectory — all required for BootstrapLauncher to
                 // resolve cpw.mods.securejarhandler as a module.
+                // Forge manifest JVM args also contain "-cp ${classpath}" — we resolve
+                // it here so the manifest's -cp takes precedence (avoids duplicate -cp
+                // issues and ensures the manifest controls the final classpath).
                 if (manifest != null) {
                     Map<String, String> vars = buildVariableMap(options);
+                    vars.put("classpath", cpFile);
                     for (String arg : manifest.getJvmArguments()) {
                         command.add(resolveVariable(arg, vars));
                     }
@@ -500,8 +505,8 @@ public class LaunchCommandBuilder {
             // through Forge's own module system (securejarhandler + module path).
             // Having them on the classpath creates automatic modules that conflict
             // with Forge's own module layer (split-package ResolutionException).
-            if (isForgeLike && (lib.name.startsWith("net.minecraft:client") || lib.name.contains("minecraft"))) {
-                System.out.println(ZAnsi.cyan("  Skipping Minecraft lib: " + lib.name));
+            if (isForgeLike && lib.name.startsWith("net.minecraft:")) {
+                System.out.println(ZAnsi.cyan("  Skipping Minecraft lib (loaded via module system): " + lib.name));
                 continue;
             }
             Path libPath = lib.artifactPath != null ? librariesDir.resolve(lib.artifactPath) : null;
@@ -545,12 +550,22 @@ public class LaunchCommandBuilder {
 
         Path versionJar = findVersionJar();
         if (versionJar != null) {
-            if (isValidJar(versionJar)) {
-                paths.add(0, versionJar.toAbsolutePath().toString());
-                System.out.println(ZAnsi.green("  Added version jar: " + versionJar.getFileName()));
+            // For Forge/NeoForge: do NOT add version jar to classpath.
+            // Forge loads Minecraft classes through its own module system
+            // (securejarhandler + BootstrapLauncher module layer). Having the
+            // version jar on the classpath creates an automatic module (e.g.
+            // _1._20._1) that conflicts with Forge's "minecraft" module,
+            // causing ResolutionException split-package errors.
+            if (isForgeLike) {
+                System.out.println(ZAnsi.cyan("  Skipping version jar for Forge/NeoForge (loaded via module system): " + versionJar.getFileName()));
             } else {
-                System.out.println(ZAnsi.yellow("  Corrupt version jar, deleting: " + versionJar.getFileName()));
-                Files.delete(versionJar);
+                if (isValidJar(versionJar)) {
+                    paths.add(0, versionJar.toAbsolutePath().toString());
+                    System.out.println(ZAnsi.green("  Added version jar: " + versionJar.getFileName()));
+                } else {
+                    System.out.println(ZAnsi.yellow("  Corrupt version jar, deleting: " + versionJar.getFileName()));
+                    Files.delete(versionJar);
+                }
             }
         }